I. Field of the Invention
The present invention is related to an electrotherapy apparatus of the type used for transcutaneous electrical nerve stimulation. In particular, the present invention relates to an electrical device which generates a squarewave output signal having a constant predetermined current which is independent of the resistance of the section of the body to be treated.
II. Description of the Prior Art
The use of electromagnetic radiation for medically treating sick or injured patients is well represented in the prior art. For example, diathermy treatments were originally developed to utilize the heating effect of high frequency electromagnetic energy in order to treat muscular disorders. More recently X-ray and gamma radiation have been utilized in the control of malignant tumors such as cancer.
The recent introduction of acupuncture medical techniques has stimulated medical research as to the operative medical connection between the nervous system and the normal functioning of other body organs. The results of this medical research indicates that the functioning of and pain sensation produced by many of the body organs may be regulated through the appropriate stimulation of various multiple nerve endings spaced generally away from the particular body organ.
Some medical reserachers have endeavored to combine the teachings of electromagnetic medicine with the teachings of acupuncture medicine, thus resulting in the field of auriculotherapy. One early pioneer in the field of auriculotherapy was Dr. Paul Nogier of France who recognized that certain body conditions could be treated through the application of electrical energy to nerve endings in the ear or auricle. At the present time the typical auriculotherapy device includes a bipolar probe which is utilized to compare the impedance of the human cell tissue between a central point on the bipolar probe and a reference point on the human body with a second point on the bipolar probe and the same reference point, typically a hand-held ground reference potential. Auriculotherapy researchers have recognized that nerve endings typically have lower tissue resistance than the surrounding skin. It is therefore important to locate with sufficient accuracy the nerve endings corresponding to the body organ or area to be treated. Typically the resistance between a key acupuncture point and the reference potential may be on the order of 900 kilo-ohms, while the resistance measured between the surface of the skin not adjacent to a key acupuncture point and the reference potential would be on the order or 1,500 kilo-ohms.
After the impedance differential method has been utilized to locate the key points, the same bipolar probe is typically utilized for applying a low frequency pulsating signal across the acupuncture point. The typical auriculotherapy device applies a known voltage across this impedance in order to develop the flow of a small current through the nerve to be treated, typically on the order of 20 to 100 microamperes.
Since the actual impedance of the different acupuncture or key points as measured across the two elements of the bipolar probe could vary by as much as a factor of 10 depending upon the precise nature of and location of the acupuncture point, the actual current which flows through the acupuncture point cannot accurately or easily be determined. Since recent medical research has revealed that the waveform of and the effective integrated average of current are primarily related to the effectiveness of the application of this electrical energy to the acupuncture points, it has become even more important to accurately regulate the flow of electrical current through the acupuncture point.
While medical research regarding the use of electrotherapy and acupuncture are continuing, up to the present time there has been no definitive consensus as to the effectiveness of this mode and technique of treatment. Therefore, while the Federal Food and Drug Administration has not yet approved this modality of electrotherapy, the FDA has nevertheless agreed not to exert jurisdiction over devices which employ output currents of less than 500 microamperes. Recent medical research, however, has indicated that the level of 500 microamperes of current is more than sufficient for treating the typical patient.
Several different theories have been proposed as to the effectiveness of the electrotherapy techniques. The most simplistic of these theories postulates that the electrical signal applied to the nerve ending merely overloads the nerve and thereby jams the brain's sensing of pain. This theory accounts for the effectiveness of stimulating the corresponding peripheral nerve in the ear as well as the effectiveness of stimulating the corresponding nerve communicating with the section of the patient's body. Not only may these techniques be used for controlling pain, but electrotherapy may also be used to recapture lost motor control of the type experienced in diseases such as Multiple Sclerosis. It has been postulated that the sustained improvement which follows the application of the electrical current to the appropriate acupuncture response point is due to a transient chemical phenomenon which in essence depolarizes the nerve endings in order to increase the output of certain chemicals in the nerve cells. This electrical stimulation improves the synaptic transfer in addition to the transfer of motor commands from the neurons to muscle tissues. See for example, KASLOW & LOWENSCHUSS, Multiple Sclerosis: Rehabilitation Through Acupuncture-Response Point Therapy, AM. J. ACUPUNCTURE (Vol. 2, 1974).
Holt, in U.S. Pat. No. 3,718,132, discloses the use of an electrical circuit for generating positive and negative pulses whose vectorial sum is equal to zero. The pulses are applied to the patient through a transformer in order to avoid any shock hazard. The voltage input to the primary winding of the transformer is held constant in an attempt to maintain a constant current output from the transformer. The output voltage is not compensated for variations in the actual impedance of the sections of the body into which the electrical energy is coupled.
In contrast to the prior art references which relate to auriculotherapy, the present invention is specifically designed for transcutaneous nerve stimulation which relates to the direct stimulation of nerves and nerve endings which are proximately related to the location of the section of the body exhibiting pain or nerve impairment. Other critical areas of the body which contain sympathetic nerve endings may also be treated with some success. The advantage of using transcutaneous neuroelectric stimulation (TENS) lies in the fact that the patient may apply this treatment himself rather than requiring the assistance of skilled medical technicians as is the case for auriculotherapy. Furthermore, the accuracy of placement of the electrode pads which impart the electrical signal in (TENS) is noncritical compared to the fine tolerances which must be maintained for the application of the electrical signal in auriculotherapy.
TENS uses the same basic concept as auriculotherapy in order to stimulate the nerve endings or synaps. This electrical stimulation produces an electrochemical change at the nerve endings close to the skin. Positive and/or negative charges travel through the sensory nerves to the brain. The presently preferred method uses a periodic waveform having both positive and negative excursions with the net total dc current equal to zero. This waveform effectively neutralizes any electrical imbalance in either the nerve pathways or in the brain.
By utilizing pads having relatively large surface areas, as compared with the smaller bipolar probes used in auriculotherapy, the patient is able to stimulate a larger number of nerve endings, or in the alternative to lessen the accuracy required in locating the nerve endings. By placing the pads on opposite sides of the body sections to be treated, the patient or operator will improve the probability of operatively coupling with a sympathetic nerve ending which is coupled to the muscle or body organ for which treatment is intended.
Thus, the first object of the present invention is to provide an electrotherapy apparatus and apparatus which utilizes paired pads for coupling a squarewave signal of constant current density for stimulating nerve endings adjacent to the area of the body to be treated.
A second object of the present invention is to provide means for regulating the frequency of the squarewave output signal and to regulate the waveform of the output signal so that it generally exhibits a 50 percent duty cycle with no dc component.
A still further object of the present invention is to provide an indicator signal for indicating when the constant current output of the device is equal to the prescribed current setting.